A method for assessing mitral regurgitation is already known from the publication entitled “Hemielliptic Proximal Isovelocity Surface Area Method Modified for Clinical Application, More Accurate Quantification of Mitral Regurgitation In Doppler Echocardiography” by HIROKO FUJI et al.”, in Japanese Circulation Journal, Vol. 65, September 2001, pages 820-826. According to this publication, the Proximal Isovelocity Surface Area (PISA) method is used for quantitative estimation of the mitral jet regurgitation. The PISA shape is chosen hemielliptic rather than hemispheric on a slit-like orifice, because the hemielliptic method is more accurate than the hemispheric method for in vitro studies. Nevertheless, the hemispheric method is used clinically because of its simplicity, whereas the hemielliptic method is difficult to approach from 3 orthogonal directions. The publication in reference presents a modified approach for use in clinical applications. A closed circuit, constant flow system was designed to simulate PISA, and various types of slit-like orifices were selected. Three orthogonal PISA radii were measured and flow rates were calculated using the original hemielliptic formula using the three orthogonal PISA radii. Flow rates were also calculated indirectly using a linear regression formula, and PISA radii from a bird's eye approach and lateral approaches (modified hemielliptic method) were compared. Flow rates that were determined using the original hemielliptic method correlated significantly with actual flow rates. Similarly, flow rates calculated using the modified hemielliptic method correlated significantly with actual flow rates. So, the study results imply that the proposed modified hemielliptic method could be used in clinical applications.